1. Field of the Invention
The present invention generally relates to data communication, and more particularly, to a data communication system in which data is exchanged via a network and a data communication terminal that can transmit/receive data and store the data.
2. Description of the Related Art
As demand for data communication increases, more data are transmitted at higher speeds via networks. Especially, data communication via mobile communication systems is rapidly developing. Users of multifunctional mobile communication terminals download a large amount of data such as music, motion picture, and application programs and store the downloaded data into their mobile terminals. Communication terminals are usually provided with large memory capacities.
However, the memory capacity of a communication terminal may not be large enough, and especially, the memory capacity of a mobile communication terminal may be still limited in order to reduce its weight, for example. When new data are to be stored in a communication terminal, the communication terminal may not have sufficient memory available for the new data.
While storing the new data in a memory, the communication terminal may determine that no memory area remains in the memory. In such a case, there may be the following options:
(a) the communication terminal continues storing the new data overwriting old data stored in the memory; and
(b) the communication terminal discontinues storing the new data leaving the old data as is.
If the communication terminal determines that the remaining memory capacity available for the new data is not sufficient before the communication terminal starts storing the new data, there may be the following options:
(c) the communication terminal deletes old data stored in the memory and secures memory area for the new data to be stored;
(d) the communication terminal moves the old data stored in the memory to a secondary memory to secure memory area for the new data to be stored; and
(e) the communication terminal sends the old data stored in the memory to a data storage server via the network to secure memory area for the new data to be stored.
In the case of a mobile communication terminal, because a user may not carry such a secondary memory with her, it is probable that the user uses the data storage server connected to the network.
FIG. 7 is a schematic diagram showing an exemplary data communication system. The data communication system shown in FIG. 7 includes a mobile communication terminal 101, a station 102, a data communication network 103, a voice communication network 104, a data storage server 111, and a data distribution server 112. The mobile communication terminal 101 is connected to the station 102 via a radio channel. The station 102 is connected to the data communication network 103 via a wired channel. The station 102 is also connected to the voice communication network 104 via a wired channel. The access method between the mobile communication terminal 101 and the station 102 may be frequency division multiple access (FDMA), time division multiple access (TDMA), or code division multiple access (CDMA), for example. Transmission speed of a mobile communication terminal can generally be defined by the number of frequency channel (in the case of FDMA), the number of time slots (in the case of TDMA), and the number of spreading codes or spreading factor (in the case of CDMA).
The station 102 is positioned between the mobile communication terminal 101 and the data communication network 103 and between the mobile communication terminal 101 and the voice communication network 104. The station 102 converts and translates radio communication signals to wired communication signal, and vice versa. The station 102 further controls radio channels and wired channels. That is, the station 102 can assign a frequency channel, a time slot, or a spreading code to the mobile communication terminal 101 in accordance with the communication method between the communication terminal and the station. Data is transmitted through the data communication network 103, while voice signals are transmitted through the voice communication network 104. An example of the data communication network 103 includes the Internet and a local area network (LAN). Multiple communication terminals and multiple servers can be connected to the data communication network 103. The data storage server 111 and the data distribution server 112 are examples of the multiple servers connected to the data communication network 103.
FIG. 8 is a block diagram showing a conventional mobile communication terminal. The mobile communication terminal 101 includes a radio transceiver 201, a control unit 211, a memory unit 212, a microphone 221, a speaker 222, a keyboard 223, and a display unit 224. The mobile communication terminal 101 may further include a digital camera unit (not shown) and a radio/television broadcasting receiver unit (not shown).
The control unit 211 controls the entire system of the mobile communication terminal 101. The radio transceiver 201 receives the data and the voice signal transmitted through the data communication network 103 and the voice communication network 104 via the station 102. The received voice signal is output from the speaker 222, and the received data is stored in the memory unit 212. Voice input to the microphone 221 is converted into a voice signal, and the voice signal is transmitted to the voice communication network 104 through the radio transceiver 201. Similarly, data stored in the memory unit 212 can be displayed on the display unit 224, or transmitted to the data storage server 111, for example, via the data communication network 103.
FIG. 9 is a schematic diagram for explaining the transition of screens shown on the display unit 224 of the mobile conventional communication terminal 101. In an initial state, a user can use the keyboard 223 and the display unit 224 to input data or select options regarding new data stored from now on or old data stored in the memory unit 212. When the user selects “NEW DATA SETTING” while the initial screen is shown on the display unit 224, a screen for new data setting 302 is shown on the display unit 224. Using the screen for new data setting 302, the user can set “OVERWRITE” ON, which means that, if memory capacity becomes insufficient while storing new data in the memory unit 212, it is not suspended, and the old data stored in the memory unit 212 is overwritten with the new data. If “OVERWRITE” is OFF, it is suspended without overwriting the old data when the memory capacity of the memory unit 212 is exhausted.
On the other hand, when the user selects “STORED DATA LIST” using the keyboard 223, a screen showing stored data list 321 is shown on the display unit 224, where the user can input various parameters and/or select options. For example, the user can designate a data storage server 111 (FIG. 7) to which the user move data stored in the memory unit 212 while a screen for storage server setting 323 is displayed on the display unit 224. According to an embodiment, the data storage server 111 may require prior registration of the user and the input of appropriate account name and password by the user. The user can select a single data storage server 111 in which all data stored in the memory unit 212 is stored in common, whereas different data stored in the memory unit 212 may be stored in different data storage servers (not shown).
When the user selects “PROTECTION SETTING” while the screen for stored data setting 322 is displayed, a screen for protection setting 324 is displayed on the display unit 224. The user can turn “PROTECTION” ON and OFF, which means that the data stored in the memory unit 212 is protected or not, respectively, when new data is stored and the old data stored in the memory unit 212 is overwritten. These settings are also stored in the memory unit 212.
If the user permits to overwrite the old data stored in the memory unit 212 with the new data, the user turns “OVERWRITE” ON. If the user does not want some of the old data stored in the memory unit 212 to be overwritten, the user can set “PROTECTION” ON in the screen for protection setting 324, which leads that the old data with “PROTECTION” ON is not overwritten even if the other old data is overwritten. If all of the old data stored in the memory unit 212 is set “PROTECTION” ON, and the memory capacity available for the new data is exhausted, it is suspended to store the new data. If some of the old data stored in the memory unit 212 is not set “PROTECTION” ON, and the memory capacity of the memory unit 212 available for the new data is exhausted, the oldest item, the least frequently accessed item, or the most previous item of the stored data may be selectively overwritten. The user can implement such settings manually, or the setting may be implemented during the assembly process of the mobile communication terminal 101.
If the user desires that the old data stored in the memory unit 212 be moved to the data storage server 111 connected to the data communication network 103 in advance, the user selects the old data that the user desired to move to the data storage server 111 using the screen showing stored data list 321. The user then designates the data storage server 111 to which the user desires to move the selected old data using the screen for storage server setting 323. When the user selects “MOVE”, the communication terminal is connected to the network, and the selected old data stored in the memory unit is uploaded to the designated data storage server 111 through the upstream channel.
Japanese Patent Laid-Open Application No. 2002-236641 discloses a system in which a mobile communication terminal requests a server to transmit content stored therein at a transmission speed via a data communication network, and the server transmits the requested content to the requesting mobile communication terminal at the requested transmission speed.
When the mobile communication terminal 101 of the communication system shown in FIG. 7 downloads new data, the mobile communication terminal 101 can move the old data stored in the memory unit 212 to the data storage server 111 connected to the data communication network 103 before starting the download of the new data thereby to secure the memory capacity for the new data to be downloaded. If the amount of the new data to be downloaded is not known, it may be difficult to secure the memory capacity of the memory unit 212 for the new data in advance. Additionally, in the case of a communication system in which the transmission speed of downstream channel is larger than that of upstream channel, it may be not possible to move the old data to the data storage server after starting the download of new data. The remaining memory capacity of the memory unit keeps being reduced, and the download of new data may be suspended.
In the case of the system described above in which a mobile communication terminal designates transmission speed, if the mobile communication terminal can not check the remaining memory capacity of the memory unit in which downloaded new data is stored, it may be practically difficult to secure the remaining memory capacity by uploading the old data to the data storage server.